Beacon receiver means



July 6, 1948. D. D. GRIEG l-:rAL 2,444,439

BEACON RECEIVER MEANS Filed March 26. 1945 2 Sheets-Sheet 1 OIVAL 0 0. GRIEG HL EIA/V067? FRI/M BY l 5 TER DUB/N 7 AmR/VEY July 6, w48. D. D. GRIEG Erm. 2,444,439

BEACON RECEIVER MEANS Filed March 26. 1945 2 Sheets-Sheet 2 nHI. lo g @a hIH*- ges BEACON REC i;

Donald D. Grieg. New York; and

i R MEANS Forest Hills, Alexander Frum, i l i Dubin, Brooklyn, N. Y.,

assignor to Fede Telephone and Radio Corporation, New York, N. Y., a corporation of Belaware Application roll 28, 1945, Serial No. 584,862

This invention relates to radio beacons and more particularly to receiver means for indicating its location relative to a beacon of the rotary signalling type.

In the copending application of E. Labin and D. D. Grieg 92-104, Ser. No. 581,974 tiled: March l0, 1945, therelhas been described a visual indicator beacon system which is applicable to various modulation methods and wherein all positional informtion is presented by means of a direct viewing meter unit which may, for instance, be located on the dashboard of an air-l craft for determining directional position with respect to areference base.

In the beacon system of the above-identified copending application, the radio beam is modulated in synchronism with its rotation about the transmitter position, the modulation being such that continuous indications may be had from the indicator at the receiver station in contrast to indications by azimuth segments as in some previous systems. In order that the bearings obtained with such a system remain independent of supply voltage changes, input and output signal changes, and so forth, the transmitter and receiver signals are in rthe form of ratios rather than absolute signal values. The meter indicator at the point of observation is a special ratiometer device which is not affected by variations in the absolute levels of these signals. By this means the accuracy of the system may be maintained independent of the operating param-e eters.

It is an object of this invention to provide for an omni-directional radio beacon system of the above described type. apparatus suitable for op, erating an indicator for signal ratios.

It is a further object to provide controls for a signal ratio indicating device which will serve to render the indications thereof dependent on the beginning and the duration oi.' the signal or seam encountered by the receiver.

It is still another object to provide means for a signal ratio indicating device which will main- :ain the last indication until a revised bearing it the next-beam interception is obtained.

Inaccordance with afeature of this invenzion, we provide areceiver with a special indi- :ation uni-t for use in a radio beacon system hav- .ng altransmitter emitting three signals over a rotating directional antenna wherein two oi the signals are modulated in amplitude in synchroiism with the rotation of the antenna and the ;hird is of constant amplitude. As the beam gasses the receiver antenna, an interpretation of the signals in terms of position with respect to the transmitter location is directly given. The indicating device used with the receiver is a ratiometer, consisting of two coils placed at an angularity of degrees with respect to one another. In order that the ratiometer needle may be made to move through 360 degrees, it is necessary that one of the ratiometer 'coils be supplied with a voltage which is proportional to sine e, and the other coil is supplied with a voltage proportional to cosine 0. For any particular value of o, then the needle will align itself with the resultant magnetic field which will lie at an angle. 0, with a fixed reference direction. Since the circuit feeding the ratiometer consists essen-tially of a detector which can furnish signals of only one polarity it Ibecomes necessary to transmit three signals which are proportional to (A+-Sine 0), (A+Cosine 0) and A, respectively, where 01s the angle that the transmitter antenna makes with a fixed reference direction and A has a value equal to or greater than unity. In the ratiometer circuit the value A is subtracted from each of the other two values yielding the desired sine and cosine functions.

As the signal from the transmitter passes the antenna of the plane, the field strength increases until such time as the transmitter antenna is pointed directly at the plane and then decreases this field strength variation being symmetrical about the maximum value. The width of this beam is of course, dependent on the distance of the plane from the transmitter, which may be located either on land or on a ship. During the time the signal is being received, the transmitter antenna is changing its position and therefore `the information received is varying with the angle of the antenna. Special circuits are provided to integrate the signal over the width of the beam so that the nal signal is made proportional to the center thereof and to rotate the meter pointer to the correct bearing indication. This electrical infomation is maintained on the meter until the next bearing is received.

These and other objects and features of the invention may be better understood from the detailed description made with reference to the accompanying drawings, in which:

Fig. l is a diagram in block form of a beacon transmitter for use with our invention;

Fig. 2 is a diagram in block form of a receiver circuit incorporating 'our invention; and

rFig. 3 is a, diagram showing partly in schematic form the receiver circuit portion of Fig. 2 incorporating our invention.

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Referring now to Fig. i, there is shown a transmitter circuit comprised of three separate oscillators I. 2 and l which are designed to produce oscillations having the frequencies F1, F2 and F3, respectively.

f these, the signals from oscillators I and 8 are subjected to a continuous modulation which is synchronized with the antenna rotation by a motor 4 which drives both the antenna 5 and the vario-coupler modulator circuits 6 and 1. The signal of the second oscillator, which remains at a constant and unmodulated value is then combined with the two modulated signals in a mixer circuit 8, the composite signal modulating the final transmitted signal in the modulator and radio frequency transmitter 8.

In the block diagram of Fig. 2, is shown a receiving antenna I0 which is applied to a receiver II.y The composite signal as picked-up by the antenna I0 is broken down into components by means of band pass filters I2, I3 and I4 in accordance with their respective frequencies F1, F2 and F3. The three signals, are now amplified in the amplifiers I5, I6 and I1 and subsequently applied to the detector integrator circuits I8, I9 and 20. After obtaining the detected signals, of which the two originally modulated signals still retain their modulating uni-directional envelope and the unmodulated signal is subtracted from each in the subtracting circuits 2l and 22 to result in two modulated currents which are fed into the coils of a ratiometer 23. Relay circuits 24 which are energized by means of the amplified unmodulated signal, control the operation of the detector-integrator circuits and of the subtracting circuits explained hereinafter in detail in connection with Fig. 3.

Referring now to Fig. 3, it may beseen that the circuits for the three signals which are generally identical comprise after each of the amplifiers I5, I6 and I1 integrator-detector circuits which consist of electron charging tubes 25, 26 and 21, to the grids of which the respective signals are applied for the control of the plate currents thereof. The respective tubes are suitably biased by means of cathode resistors 26, 29 and 30 to give them a large impedance and provide them with detector or rectifying characteristics. The tubes are connected to ground through integrating condensers 3l 32, 33, respectively. The voltages to ground of the integrating condensers are applied to the grids of two pairs of triodes 34, 35 and 36, 31, the voltage due to the non-modulated signal being applied to the grids of two of the triodes, 35 and 36. The cathodes of the triodes 34, 35, 36, 31 are provided with cathode biasing resistors 36, 39, 40, 4I and connect to ground at 42 through a relay controlled contact 43. The anodes of each pair of the triodes are connected to the opposite terminals of one of the two field coils 44, 45 respectively which are disposed in a 90 degree angularity with respect to one another and provide the eld governing the indication of the ratiometer 23 (see Fig. 2). An indicator 46 is suitably mounted on an armature coil or magnet 41, which receives its turning moment from the resultant magnetic held of the coils 44 and 45 and servesrto indicate the desired direction in degrees from a given null position. The operability of the two pairs of triodes as well as that of the detector-integrators is made dependent upon the presence of a signal from the amplifier I6, which is given suitable amplication in the triode 48 and the tetrode 49 to provide an energizing current for a master relay 50 which operates a double action contact 4I and 43. Contact 8|' controls the energization of a slave relay 62 which in turn operates a triple contact 6I serving to by-pass to ground the integrating condensers 3l. 32, and 33.

The operation of the system as a whole is described in the copending application, Labin-Grieg 92-104 Ser. No. 581,974, above referred to, and therefore will be recapitulated here only briefly. The vario-modulators (Fig. 1) may comprise two stationary coils with a relative degree angularity and a rotary coil. The rotary coil is rotated together with the antenna 5 so that its angle of displacement 0 from a given null or reference point is also that of the rotated antenna. The three oscillators supply signal energy prei'- erably at audio frequencies which substantially may be expressed as A sine 21rF1t, A sine 21rFat, and A sine 21rFat. The stator coils induce a voltage in the rotary coil of the vario-modulator which varies synchronously in amplitude with the rotation of the rotary coil. Due to the physical arrangement of the two stator coils the amplitude variations of the two voltages induced in the rotary coil are 90 degrees out of phasev that is one is a sine, the other a cosine function of the angle 0. The constant amplitude current of the stator coils and the varying amplitude current of the rotary coll are combined so that an A-l-sine function of the one frequency and an A-f-cosine function of the other frequency is finally obtained; the final expression of the three signals as ultimately brought together in the mixer 8 is as follows:

(A4-sine 0) sine 21rFit (A-i-cosine 0) sine 21u-Fat A sine 21rFt where AE1 The composite signal which is the sum of the three above-described functions is broken down again in the receiver Figs. 2 and 3, into its constituent components through the medium of the respective band pass filters I2, I3, and I4 as indicated in Fig. 2. After amplification and detection, a signal voltage is obtained for the first and third signals which consists of a sum of the second signal A and signals proportionate to the sine and cosine functions respectively, that is, they may be expressed as A+sin a and A-i-cos 0. This second signal A is then subtracted from both of these signal voltages in the subtracting circuits 2| and 22, the resulting signals becoming directly proportional to the pure sine and cosine functions of the angle o. The output of the two ratiometer coils 44, 45 causing the deflection of the indicator coil 41 is proportional to the quotient of these two functions, that is, it equals the function tan 0.

Since the highly directive rotary signal beam from the transmitter has a relatively' short duration at any one time with respect to the receiver, it is clear that if the signal voltages due to such a beam were applied directly to the ratiometer the rotary coil 41 would vary in position over the width of the lbeam starting with the leading edge thereof in the receiver when it first becomes sensitive and stopping when the beam passes the receiving antenna.. Such an indication then, instead of giving a direct line to the beacon transmitter would rather indicate the edge of the beam. It would be diihcult under these circumstances ifor the pilot or operator to read the midpoint of the pointer swing. It is therefore desirable to provide some means which 'will indiattacca cate sumciently the mid-position of the beam. In the present system this beam center rlnder system comprises the detector integrator circuits 25--3I for the first signal, and the analogous circuits for the other two signals. Thus the to ground to improve their integrating characteristics. The energy is applied across each of the vacuum tubes and thus serves to charge each of the condensers, the plate current being alinear function of the grid voltage. This charging` of the condensers occurs for the time during which the beam is received. The integrated voltage en-y ergy is then applied to the grids of the electron discharge tubes 34, 35, and 36, 3l in the subtracting circuits which serve to supply energy to the ratiometer coils 44 and 45. Since thewidth of the lbeam and hence the time of integration is a function of the distance between the transmitter and the receiver, the voltage to which the integrating condensers will charge may vary according to this distance. It is necessary therefore tolilnit the maximum voltage which is given by the dissipation characteristics of the output tubes when the beam may be expected to be at its widest. For normal operation the mid operating point is selected for a voltage which corresponds to the integrated constant amplitude signal with equal positive and negative values for the grid swing in respect to the selected mid-operating 'condensers will be substantially proportional so that the ratio of the energy supplied to the ratlometer coils will remain constant. However, it is necessary, to discharge the storage condensers every time that the beam is about to pass the antenna, in order that the new values of the condenser voltage may represent the ratio of the energies in the next beam and not a cumulative effect produced .by a number of passages. The

' electron charging tubes which serve as the high impedance must also be de-energized whenever Y the beam energy is not being received so that their continued operation will not keep up the charging of the condensers to the poin-t where grid current will be drawn by the following tubes '34, 35, 3B and 31. i

To accomplish these purposes, the two relays 55u and 52 are provided. The master relay 50 is arranged to` operate immediately the beam energy is received and a predetermined voltage level is exceeded and establishes a plate potential for the three impedance tubes 25, 26 and 21 over contact 5l.

In the present system where three signal energy components are used, the reference frequency of the second signal serves. the purpose of operating this relay. since it is not modulated in accordance with azimuth at the transmitter. At the same time that the master relay 50 closes the plate circuit for the'impedance tubes it also closes the circuit 5| for energizing the slave relay 52.

are produced upon the closing of the master relay circuit. This relay pulse closes the contacts Bt to short-circuit to ground the three storage con" densers 3l, 32 and si. As soon as the transient passes through the relay coil a time-constant circuit in the return thereof is charged so that the relay again drops to permit the condensers to charge up in accordance with the new beam sign nais. As the beam passes the receiving antenna the master relay 5@ drops to cause de-energization of the impedance tubes so that the condensers will not be further charged and permitting them to retain their storage voltage until the nent beam action crosses the antenna path. At the time when the relay 50 is energized, that is, during the presence of the signal and at the time that the integration takes place, the cathode circuits of the impedance tubes are disconnected by contact t3. Accordingly, no energy will be supplied to the ratiometer coils until a ratio corresponding to the integrated beam signal, that -is, until the beam center has been attained. This results in a return movement of the indicator each time the beam passes, thereby/giving an assurance of in dlcator operation.

Referring now to the mixer or subtracting c ircuits and the ratiometer, there is normally a direct current plate voltage applied to the coils M' and t5, which are disposed at right angles to one another, and to the four output tubes 3c, 35, 36 and 3l. The tubes are biased in such a way that normally when the-plate voltage is applied the tubes carry current. But since this plate voltage causes equal current ilowing into the opposite ends oi' the two ends of the ratiometer coils, the coils are maintained at a zero resultant potential. The voltages due to the -beam signal are applied to the grids of the outside tubes til and 3l, the anodes of these tubes being connected to one end of coils M and l5 respectively. The grids of the tubes 'and-36 are connected for the applica-l tion thereto of the steady voltage of the middle' or'second signal circuit. The anodes of these' inner tubes are connected to the other ends of the coils M and l5 respectively. Consequently, there will be produced across these coils a voltage equal to the differences between the signals made'up of the constant voltage Vand of the sine function', and of the constant voltage, and of the cosine function and the steady voltage function respectively. As a result the voltage across these two coils will vary positively and negatively relative to their normal value so that a complete 360 degree turning effect may be obtainedvon the indicator coil M.

Preferably, cathodes of the output tubes are biased by the provision of cathode resistors in order to assure considerable negative feedback andto maintain the tubes at sucbA low amplification that they will not draw grid current thus tending to discharge the integrating condensers connected to the inputs, whenever the storage of the beam signal is desired as outlined above.

While we have shown our invention embodied in a specific form and ln connection with specic signal characteristics, it is clear that other types of signals and appropriate circuits may be provided. It should therefore be understood that modifications and variations in this system in accordance with our invention may occur to those skilled in the art. The particular embodiment given above is presented merely .by way of illustration and should not be considered as a limitasansa tion i our invention as set lorth in the objects thereof and in the appended claims.

We claim:

1. In combination with a ratiometer device having two field coils placed at an angle with respect to one another for producing an operating magnetic'ileld, means -ior supplying a first composite voltage made up oi a first signal and oi a,

second signal, means for supplying a second composite voltage made u'p ot a third signal and of said second signal. means for supplying said second signal. circuit means for effecting a subtraction of said second signal from said first composite voltage and fromsaid second composite voltage, and means for applying the two resulting diierential signals of said last named means to the said two field coils, respectively.

2. In combination 4with a ratiometer device having two field coils placed at an angle of 90 degrees with respect to one another for producing an operating magnetic-field, means -for supplying a rst composite voltage made up of a ilrst signal modulatedy as the sine of the angle of departure from a base of a continuously rotating reference vector and of a constant amplitude second signal, means for supplying a second composite voltage made up of a third signal modulated as the cosine of the said angle and of said constant second signal, means for supplying said second constant signal, circuit means for subtracting said second signal from said iirst composite voltage and from said second composite voltage, and means for, applying the resulting diierential signals of said last named means to the said two ileld coils respectively.

3. A combination in accordance with claim 2, wherein said first, said second and said third signals comprise different base frequencies and the three ilrst named means include demodulators for said three signals respectively.

4, A combination in accordance with claim 2, further including means for providing a signal voltage corresponding to the center of a beam signal having a given leading and a given trailing edge in respect to time including a voltage integrator circuit.

5. A combination in accordance with claim 2, wherein the three rst named means include voltage integrator circuits, the combination further including operability control means for said integrator circuits controlled by thepresence of a signal voltage.

6. A system for operating a ratiometer comprising. means for supplying a first composite voltage made up of a first signal modulated as the sine of the angle of departure from a base of s. continuously rotating reference vector and.

of a constant second signal, means for supplying a second composite voltage made up of a vthird signal modulated as the cosine of the said angle and of said constant second signal, means for supplying said second constant signal, means for integrating each of said composite voltages and said constant signal, means for controlling the operability of said integrator mea/ns responsive to the presence of a given signal, and means for operatively applying the output of the given signal.

9. A system for operating a ratiometer type indicator including two field coils placed at an angle of degrees with respect to one another 4form producing an operating magnetic ileld for an indicator thereof, comprising means for supplying a iirst composite voltage made up of a first signal modulated as the sine of the angle of departure from a base of a continuously rotating reference vector and oia constant second signal, means for supplying a second composite voltage made up of a third signal modulated as the cosine of the said angle and of said constant second signal, means 4for supplying said second constant signal circuit means for subtracting said second signal from said ilrst coinposite voltage and from said second composite voltage, means for controlling the operability o! said circuit means responsive to the presence of a given signal, and means for applying the resulting differential signals of said circuit means to the said ltwo field coils.

10. A system according to claim 9, wherein said circuit mea/ns comprises vacuum tubes having their cathodes normally connected to ground,

and said means for controlling includes means, for interrupting the circuit of said cathodes to three signals each having a different -base fre--4 quency, two of said signals having differently modulated envelopes, and the third signal having a constant value, comprising a pair of electron discharge tubes for energizing each of the said coils, the plate current of the tubes oi each pair being opposed to one another in the respective iield coils and being a function of the constant signal and one of said modulated signals and of said constant signal andthe other of said modulated signal respectively, and means for controlling the operability of said tubes responsive to the presence of a signal Vfrom said source. A

13. A circuit according to claim 12`further including means for integrating the respective signals over a given period of time operatively disferent frequency and having an envelope correspending respectively to a sine function and a constant value, a cosine function and aconstant value and a constant value, comprising a pair of electron discharge tubes for energizing one of said coils, and a pair of electron'discharge tubes for energizing the other of said coils, the plate current of the tubes of each pair being opposed to one another in the respective eid coil, the plate current of one of said pair of tubes being a function of the constant value signal and said signal varying in correspondence with the sine function and a constant value, and the plate current of the other of said pair of tubes being a function of said constant value signal and said signal varying in correspondence with the cosine function and a constant value.

16. A circuit for energizing a ratipmeter device having two field coils from a source supplying three signals, each of said signals having a diff ferentfrequency, two of said signals having differently modulating envelopes, and a third signal having a constant value, comprising a pair of electron discharge tubes for energizing each o said coils, the plate current of the tubes of each pair being opposed to one another in the respective eld coil and being a function of the constant signal and one of said modulated signals and one of said constant signal and said other modulated signal respectively, means for detecting each of the said signals, and means for integrating the respective signals over a given period of time forming a part of said last named means.

17. A circuit according to claim 16, wherein said means for integrating comprises a condenser for each signal between said detecting means and ground, further including means fordischarging said condensers transiently responsive to the presence of a signal from said source. i

18. A circuit for energizing a ratiometer device having two field coils from a source supplying each of said signals preceding said tubes, means for integrating the respective signal over a given period of time comprising a condenser for each signal and forming a part of said detecting means in its circuit to ground, means for controlling the operability of said tubes andl of said detecting means comprising a double acting relay, and means for transiently discharging said condensers, said means for controlling and said means for discharging being responsive to the presence of a signal from said source.

19. A circuit for energizing a ratiometer device having two iield coils from a source supplying three signals each having a different frequency, two of said signals having differently modulating envelopes, and the third signal having a constant value, comprising a pair of electron discharge tubes for energizing each of said coils, the plate current of the tubes of each pair being opposed to one another in the respective field coil and being a function of the cosntant signal and one oi said modulated signals and of said constant signal and said other modulated signal respectively.

DONALD D. GRIEG. ALEXANDER FRUM. LESTER DUBIN.

REFERENCES CITED The following references are of record in the le of this patent:

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